User blog:Unin/FrodoTip: Mirrors?
This will hopefully be the start of a series of articles meant to address common Frodo complaints. Caution: Occasional injects of real world physics, possibly involving maths, may be involved. FRODO: Why don't they just coat everything with mirrors and reflect the lasers back at the BETA? Ignoring the logistical nightmare of trying to maintain field equipment to a perfect mirror polish, this has two major technical drawbacks. The first, and most common retort to such frodoing, is that their is no such thing as a perfect mirror. This is technically true, but considering modern real-world lasers are routinely generated, guided, and manipulated by mirrors, it's easy to see how further frodoing would ensue and devolve into and optics efficiency and heat transfer argument boiling down to who's got the biggest math peen. That said, even with 99.999% efficient mirrors used in highend real-world laser etching setups, you still have SOME heat absorbed and transferred to the mirror. Over time, this can lead mirror warping, or thermal expansion damaging mirror gimbals and galvanometers. Now imagine putting it up against intensities capable of nearly instantly vaporizing cubic meters of military grade aircraft alloys. Coating a TSF in highly reflective coating might keep it from being slagged, but the energy that makes it through would have to be compensated for, or else you might cook the pilot. Unfortunately, the very nature of that same reflective material makes it difficult to radiate that heat away, and that's not even factoring in the heat generated from operating the TSF. Air cooling might help, but only if the TSF is moving fast enough, which requires the sort of free and clear flying space that makes a TSF a prime laser target in the first place. This only matters of course, if your mirror reflects the right type of light. The second, and most significant counter argument is that mirror are only effective for certain wavelength bands. Optical mirrors are fine and dandy for visible light, and to a lesser extent near IR and UV, but there is a reason why most research telescopes AREN'T mirrors. Outside the NIR to NUV spectrum, optical mirrors are worthless. Want to reflect IR radiation? Go for something WHITE like titanium dioxide (remember that physics lecture you slept through about white and black t-shirts absorbing heat?). Gotta block Far UV? best invest in silica carbide or lithium fluoride coatings. Need to reflect X-rays or Gamma rays? Too bad, (unless you're hit at just the right grazing angle of incidence) you're pretty much gonna have to eat it no matter what you're coated in. Most man-made lasers are coherent and monochromatic, but they don't actually have to be. There is no technical reason why a laser class BETA has to emit at one precise and narrowly defined frequency, or that both species, which by all sources are unrelated, should both emit at the same frequency. All we know is that they emit a nearly parallel beam of high intensity radiation. It could be exactly 610nm "orange", but it could also be a 550-700nm spread, peaking at 610nm. The fact that many images portray lux lasers as white could imply "its simply too intense to resolve color", or it could suggest a wideband of wavelengths that we perceive as mostly white light. For all we know, it could be an invisible high energy gamma ray laser causing atmospheric gases to ionize at whatever color the artist had on hand. If the laser class are supposed to be general purpose mining lasers, its neither impossible nor all that improbable that they would emit at a spread of wavelengths that no single material surface could reflect completely at 100% albedo, or even effectively at a mere 50%; a visible reflector may be a gamma absorber. Actually it would be to a general mining laser's advantage to be able to change wavelengths, as it encounters new materials, again rendering passive reflection useless. The ablative armor coating used on TSFs actually addresses both of these quite well, as the energy is directed into vaporizing a coating, and the expanding hot gases actually carry the heat away. This principle is used on real-world spacecraft, both for atmospheric re-entry; where air against the leading surfaces of a craft is compressed to extremely high temperatures and pressures, and for engines; which may have to handle high operating temperatures in a vacuum. Neither of these is tied to a particular frequency of light, so long as the temperature is high enough to induce ablation, and even if the ablative coating isn't a perfect black body; that just implies that some of the energy IS successfully reflected rather than absorbed. Category:Blog posts Category:FrodoTip